1. Field of the Invention
This invention relates to a method of making cross-linked polydiorganosiloxane.
2. Description of the Prior Art
Polydiorganosiloxanes can be cross-linked by many methods. Some of these methods as known in the art include, the use of organic peroxides and heat, the use of gamma radiation, the use of ultraviolet radiation, the use of moisture sensitive cross-linking species such as monoorganotriacetoxysilane with certain catalysts, and the use of compounds containing silicon-bonded hydrogen and compounds containing silicon-bonded vinyl groups in the presence of a platinum catalyst. These methods represent a few means for cross-linking polydiorganosiloxane as found in the art where these methods can be grouped into two major categories, namely heat activated and room temperature vulcanized.
Vanderlinde in U.S. Pat. No. 3,445,419 describes compositions which cure to resins and elastomers. The compositions of Vanderlinde are prepared from the reaction product of a vinyl terminated organopolysiloxane and an ester of an organic polyol and an acid of the formula HOOCR"SH. These compositions cure when exposed to air in the presence of alkali. Viventi in U.S. Pat. No. 3,816,282 describes a composition comprising a polydiorganosiloxane containing silicon-bonded vinyl radicals, a mercaptopolysiloxane, a free radical source which cures to a silicone rubber when exposed to radiation. Gant in U.S. Pat. No. 4,064,027 and Colquhoun et al. in U.S. Pat. No. 4,070,526 also describe compositions comprising vinyl-containing silicon compounds and mercapto-functional siloxanes cured by radiation.
Compositions comprising certain vinyl-containing polydimethylsiloxanes, mercaptoorganopolysiloxanes and organic peroxides which cure to elastomers at room temperature or with heating are described by Homan and Lee in U.S. Pat. No. 4,039,504, U.S. Pat. No. 4,039, 505 and U.S. Pat. No. 4,066,603.
Homan and Lee in U.S. Pat. No. 4,070,328 describe a composition of mercaptoorganopolysiloxane, organic hydroperoxide and a nitrogen compound which cures to elastomer. These inventors also describe a composition of a mercaptoorganopolysiloxane and organic peroxide which cures to an elastomer.
Bazant et al. in German Patent Publication (OLS) No. 2,008,426 discloses five different possibilities to make three dimensionally cross-linked silicone polymers. According to Bazant et al., these reactions were found to proceed in the presence of radical reaction initiators at a temperature of 30.degree. to 110.degree. C. or by UV light initiation. The five possibilities are defined as follows: One possibility is a reaction between a polydiorganosiloxane with vinyl radicals along the polymer chain and a polydiorganosiloxane with mercapto-alkyl endblocking groups. The second possibility is a reaction between a polydiorganosiloxane with vinyl radicals along the polymer chain and a polydiorganosiloxane with mercaptoalkyl endblocking groups. The third possibility is a reaction between a polydiorganosiloxane with vinyl endblocking groups and a polydiorganosiloxane with mercaptoalkyl groups along the polymer chain. The fourth possibility is a reaction of polydiorganosiloxanes which have both vinyl and mercaptoalkyl groups along the polymer chain.
The fifth possibility is reactions of high molecular thioalkylpolysiloxanes of the general formula ##STR2## where R" is an alkyl group with 1 to 6 carbon atoms, a cycloalkyl group with 5 to 8 carbon atoms or aryl groups, R'" is an alkylene group with 1 to 6 carbon atoms, the sum of p+q is greater than 30 and q/p is from 1/10 to 1/60, or high molecular thioalkylpolysiloxane of the general formula EQU HO(R"SiO.sub.1.5).sub.a (R".sub.2 SiO).sub.b {R"(HSR'")SiO}.sub.c OH
where a+b+c is greater than 5, ##EQU1## is from 1/5 to 1/60, and R" and R'" are defined above with organic diisocyanates, such as hexamethylene diisocyanate, toluene-2,4-diisocyanate, and benzene-1,4-diisocyanate. This reaction can be carried out in the aprotic solvent medium or without solvent at moderately elevated temperatures, preferably between 50.degree. and 120.degree. C. Also the addition of organic materials of a basic nature, such as tertiary amines in the amount of 0.5 to 7% by weight results in a considerable reduction in the time necessary to prepare the three dimensionally cross-linked polymer.
Siloxane sponge is known in the art. For the purpose of this application, the term sponge will be used, will mean a cellular elastomeric material and will include product types which are known as foams, for example, foam rubber. Siloxane sponge made by heating to activate a blowing agent and an organic peroxide are known. Siloxane sponge made at room temperature is also known. Bruner in U.S. Pat. No. 3,070,555 describes making a siloxane foam by mixing hydroxylated organopolysiloxane containing silicon-bonded hydrogen, a hydroxylated compound and a stannous salt of a hydrocarbon-soluble carboxylic acid and thereafter allowing the mixture to foam to an elastic product. A more recent method of making a siloxane foam is described by Smith in U.S. Pat. No. 3,923,705. Smith describes making an organosiloxane foam by mixing an organohydrogensiloxane, a hydroxylated organosiloxane and a platinum catalyst.
From the above art, it is apparent that polydiorganosiloxanes can be cross-linked by a number of ways including those which have mercapto functionality. It is also apparent that certain mercapto-functional polysiloxanes can be cross-linked with organic diisocyanates. It is, however, completely unexpected that polydiorganosiloxanes having mercapto endblocking groups can be used to make siloxane sponge or siloxane elastomers using organic diisocyanates as described below.